Where was the UK Royal Navy base Scapa Flow?

In the first and second world wars, Scapa Flow was an important naval base for the Royal Navy. It is situated at the southern end of the Orkney Islands, and takes its name from the Norwegian word "Skalpafloi", meaning "bay of the long isthmus". The surrounding islands of Mainland, Hoy, Burray, South Ronaldsay, and Graemsay afford the body of water protection from the harsh Atlantic Ocean.

It has been used to harbour ships since before the Vikings, but in WW I it was the Royal Navy's main base, the home of the British Grand Fleet. It also housed the German High Seas fleet after their surrender, but these ships were scuttled by their crews on 21st June 1919.

Scapa Flow also served as a main base for the Royal Navy in WW II, but the earlier defences were not up to the job, the German U-Boat U-47, commanded by Gunther Prein, successfully entered and sunk the battleship "Royal Oak" and then escaped. Urgent improvements to the defences followed.